How throw server side exceptions and handle them on the client?

Hi,
I'm new to Drupal, so please bare with me.

I'm creating a service mobile.whoAmI() that is to return a name of the logged in user.

The code is simple:
function mobile_service_who_am_i() {
global $user;

if (!$user->uid) {
    // User is not logged in
    return services_error(t('User is not logged in.'), 406);
} else {
    $result = new stdClass();
    $result->sessid = session_id();
    $result->user = $user->name ;

    return $result;
}

}

I have JSON-RPC server installed.

On the client I don't get any error if the user is not logged in. I tried with XML-RPC where I do get the error.
I also found this thread (http://drupal.org/node/410752) that indicates that XML-RPC was patched to take error codes into account.

My client is Android where we are discouraged to use XML-RPC.

That's why I want to use JSON-RPC, but JSON-RPC doesn't seem to create actual exception when services_error("blah", code) is used.

What is the best interface to access Drupal from mobile platform?
How can one pass exceptions from Drupal service down to the client?

Thanks.